Machine tool control



March 27, 1945.

c] JOHNSON MACHTNE TOOL CONTROL Filed Sept. 23, 1941 2 Sheets-Sheet 1 3maen tor CLARENCE JOHNSON (Ittomeg.

March 27, 1945. c. JOHNSON MACHINE TOOL CONTROL Filed Sept. 25, 1941 2 SheetS -Sheet 2 3n'nentor CLARENCE JOHNSON (Ittorneg mechanism.

, States Patent Oflice on Patented Mar. 27-, 1945 MACHINE TOOL ooN'rnoL Clarence Johnson, South Euclid; Ohio, assig'nor to Bailey Meter Company, a corporation of Dela- I ware Application September 23, 1941, Serial No. 412.018

. I Thisinvent ion. relatesto a control system for machine tools, and more particularly to a control 6 Claims. CI. 82-21) 20, 1941; respectively, of which the instant apsystem for governing therelative rate of move- 1 ment between the tool and work piece of a machine tool.

One object of my invention is to provide a. control system for a machine tool whereby the tool may be advanced relative to the work piece at a 4 predetermined speed.

A further object of my invention is to provide a control system for a machine tool" whereby the tool may be advanced relative to the work piece Still another object of my invention is to provide a control system for a lathe whereby the tool will be moved longitudinally along the lathe at a rate of speed directly proportional to the rate of rotation of the work piece. 4

A still further object of my invention is to provide a control system for a lathe whereby a thread of accurate pitch may be cut on a work piece.

Another object of my invention is to provide a control system fora lathe for advancing the tool along the work piece at a rate of speed directly proportional to the rate of rotation oi the work piece without employing a lead screw or other mechanical means subject to wear.

A further object of my invention is to provide a control system for a. lathe whereby accurate screw cutting may be accomplished without dependence upon a lead screw; the wear of which I I aiifects the accuracy of the operation.

Further objects will be apparent from the description and drawings, in which: v

Fig. 1 is a plan view of a lathe illustrating the application of myinvention thereto.

2 is.an elevation view, partially in section, of the form of pilot mechanism shown in Fig. 1.

plication is a continuation-in-part.

Referring to Fig. l, I show my invention applied to an engine lathe I having a head stock or live center 2 adapted to be rotated at desired speed by any suitablemeans (not shown) and a tail stock or dead center 3. A carriage 4 manual- 1y adjustable along the bed of the lathe in suitat a rate directly proportional to the speedof rotation of the work piece.

able ways 5 supports the tail stock or dead center 3. Also movable longitudinally along the bed of the lathe in suitable ways 6 is a carriage i. Mounted on the carriage iis a cross-slide 8 movable on ways 9 transversely ofthe bed of the lathe.

The cross-slide 8is provided with an adjustable tool support 50 in which is secured a, tool 6!.

. Transverse movements of the tool H are produced by manual adjustment. Longitudinal movements ofthe tool ii, that is movements of the tool parallel with the bed of the lathe i, are produced by means of a hydraulic servomotor generally indicated at 12, which as shown is secured to the bed of the lathe and connected by means of a piston rod l3 to the carriage i.

Supported between the head stock 2 and tail stock 3 is a workpiece on which, as illustrated, a'machine thread is being cut. In order that the thread will have a given pitch, as well known to those familiar with the art, it is necessary that the carriage accordingly the tool H,

. advance along the lat e a given amount per Fig. 3 illustrates a modified form of pilot Fig. 4 is a. control circuits employed.

diagrammatic illustration oi the v trating the application of a modified form of my 1 invention thereto. I p v Fig.6 is an isometric illustration of the form of pilot mechanism employed in theembpdime'nt of my invention illustrated in Fig. 5.

Certain features disclosed in this application are also disclosed in my copending. applications, Serial Nos. 298.290, now Patent. 2,259,472, issued October 21', 1941, and.3 84;375, filed in the United revolution of the work piec lathe such advancement is. ained by gearing the carriage, butmeans of a lead screw, to the driving shaft of the head stock. Such an ar-' rangement imposes 'a, heavy load on the lead screw however, which after a period of-time wears so that the threads are no longer accurately formed. .By my invention the carriage 'I is advanced at a speed necessary to give the thread on the work 'piece a desired pitch without a direct mechanical connection to the driving shaft of the head stock and without employing a lead screw or other means subject .to iwear. --In distinction to the ordinary means I'employ a pilot mechanism, one form of which'is generally indicated at [5 in Fig. 1, and shown to larger size in Fig. 2, whereby I establish a pneumatic loading pressure for controlling the rate of movementof the carriage I. The loading pressure so established varies from a. predetermined value, which for convenience Icall the normal value, 'in accordance with the departure of the rate of movement of thecarriage I from that desired, and such varia:-'

October 1939, and March -tions" are effective to restore the rate. of move- In the ordinary ment of the carriage 1 to that desired. Inother words, it may be said. that so long as the carriage 1 moves at the desired speed the loading pressure remains at the normal value, but upon the slightest departure from the desired speed a corresponding change in the loading pressure occurs, effective for restoring the speed of th carriage to that desired.

The pilot mechanism I5 includes difierential gears i6 and I! and wherein the internally threaded gear I! engages the external thread on gear IS. The gear I8 is secured to a spur gear i9 journaled on a shaft 19 secured to the bed of the lathe.

The split gear I8 meshes with a pinion 20 driven through a slip clutch 2| by change gears 22 and 23, the latter of which is driven from the drive shaft 24 of the head stock 2 through bevel gears 25 and 28. The outer end of differential gear l8 terminates in an annular flange I 8' extending into the groove I'I' formed in the hub oi. differential gear I1. It will thus be evident that the difi'erential gear l9 will be rotated at a rate of speed proportional to the rate of rotation of the drive shaft 24. The particular ratio between the speed of the differential gear asvama orifice 34, the pressure within thepipe 33 will have a predetermined value, which for convenience as heretofore stated I call the "normal value. Upon the'baflle 29 approaching the nozzle 32 however, the rate of discharge therefrom will decrease, causing an increase in pressure within the pipe 33. Conversely upon the baflie 29 receding from the nozzle 32 the rate of discharge therefrom will increase, causing a decrease in pressure,

within pipe 33. As will be evident as the description proceeds, so long as the carriage 1 moves at the desired speed the heme 29 will be in the posi- 33. Such deviation in pressure within the pipe However, as will be pointed out more in detail hereinafter, if an extreme of operation is reached the. diil'ere'ntial gear l4 may remain stationary while the drive shaft 24 rotates by virtue of the slip clutch 2|, thus preventing damage to the parts of the lathe which might otherwise result.

The .diiferential gear I! meshes with a rack 21 fastened to the carriage 1. As the carriage I advances along'the lathe the gear II will be rotatcd at a proportional speed. Formed integral with the end surface I'I" oi diflerential gear I! is a projection 29 engaging a baiiie 29 pivotally mounted on a support 29 secured to the bed or the lathe l and urged against the projection 28 by a" leaf spring,2l.

- When the diilerential gears l9 and i1 rotate at the same speed it is evident that the flange 12' remains intermediate the side walls of groove direction; and the baiile .29 will remain stationary.

' If,-however, the diflerential gear l6 rotates at a higher speed than the gear l1, then their relative positions are changed and the projection 28 will move axially in one direction, causing the baille 29 to be angularly positioned about its pivot support. Conversely. if the differential gear l6 roprojection 28 will move axially in the opposite i1 and the projection 28 will not move in an axial I tates at a.slower speed than the gear l1, then the direction, causing the-baiiie 29 to be angularly positioned in the opposite direction. It will be observed that the width of the rack bar 21 is such that it will always be in engagement with the gear 33 from the normal value is eflfective for controlling the servo-motor I2 to restore the rate of movement of the carriage I to that desired.

To prevent injury to the nozzle 42 and/or baiile 29, upon a material departure in the rate of movement of the carriage I from that desired, causing the baille 29 to engage the nozzle 22,1 show the nozzle 32 yieldably urged toward the bame 29 by means or a compression spring 2!. Normally the spring 35 holds a stop 28, secured to the nozzle 32, against the support 29. However, upon the baiiie 29 engaging the tip of the nozzle 32 the spring 35 will permit lateral movement, thereby preventing injury to the nozzle. 7

Pipe 39 is connected by way of a pipe 31 to an expansible bellows 39 shown in Fig. 4. The variations in pressure within pipe 21 caused by the approach and recession of baiiie 29 toward and away from the nozzle 32 control the rate of movement of a piston 29 in a cylinder 49, which piston moves thecarriage I. As illustrated, the control mechanism employed, whereby variations in pressure within the pipe 81 control the rate of movement of piston 39, and accordingly oi the carriage I, are conveniently mounted as a unit adjacent 39A which normally is partially filled with a hyv draulic fluid, such as a suitable oil. Housed within the reservoir 39A is a pump 4|A driven by a motor 4| and which is connected through a pipe 42, 4-way valve and pipe 46 to one endof the cylinder 40. The pump 4IA draws oil from the reservoir 39A through a suitable inlet pipe 49 and there may be connected to the discharge pipe 42 a relief valve 41 for maintaining a predetermined pressure within the pipe 42. The opposite end of the cylinder 49 is connected by a pipe 49, 1-way valve 44', 3-way valve 49,- pipe II and fluid resistance 5! to the oil reservoir 29A. With the 4-wayvalve 44 and 3-way valve 49 injthe position shown., it is evident that high pressure will exist on one sihe oi the piston 20 whereas apressure determined by the' resistance It will exist on the opposite side of the piston. The relation between the pressures on opposite sides or the piston 29, when the 4-way valve 44 and 3-way valve 49 a in the position shown, is such that the piston 29' moved to the right as viewed in Fig. 4, causing the carriage 1-, and accordingly the tool II, to be positioned longitudinally along the lathe. The speed with which thecarrlage 1 is positioned is varied 21,872,428 3 by varying the resistance of the fluid. resistance 5|.

The resistance 5| comprises essentially a ported body and a. movable cooperating member 52 secured to the movable head of the expansible bellows 38. When the bellows 38 is in one position the resistance'to the passage of hydraulic fluid is at a minimum, and as the bellows 38 is expanded, due to increases in pressure, the

resistance to the passage of hydraulic fluid increases proportionately. A suitable adjusting means, such as indicated at 53, may be provided so that theresistance to fluid flow produced by I the resistance 5| when the bellows 38 is at an from this extreme contracted position, the fluid resistance will gradually increase, so that when the bellows 38 is at an extremely expanded position the piston 39 and carriage 1 will remain substantially stationary. Preferably the normal value of the pressure, that is the pressure existing within pipe 31 when normal distance exists between the nozzle 32 and baflle 29 is approximately midway between theminimum and maximum pressures, effecting maximum and minimum speeds of the piston 39 respectively. Thus it will be seen that the piston 39 will be driven to the right, as shown in Fig. 4, at a speed corresponding to the pressure within'the pipe 31, which in turn will vary, depending upon the dstance existing betweefi the baflle 29 and nozzle 32. So long as normal distance exists between bafile 29 and nozzle 32, indicating that the carriage 1 is being moved at the proper speed, the fluid will pass through the resistance 5| at a constant and definite rate. Upon a movement of the baffle 29 toward or away from the nozzle 32?,

however, a proportionate change in pressure within the pipe 31 and bellows 38 will occur, causing the piston 39 to increase or decrease in speed until normal distance is restored between the baffle 29 andnozzle 32, indicating that the j carriage 1 is again proceeding at the proper speed.

In order that the tool ll maybe returned to the 'left end of its travel, I provide a hand operable lever 54 for simultaneously operating the 4-way valve 44 and the 3-way valve 49.

Thus upon the tool ll reaching the right end of its travel the tool II is withdrawn from the work piece and the rack 21 disengaged from the differential gear I1,by any suitable means (not shown). The. operator will then shift lever 54 from =.stop 55 to a stop 56. Such shifting of lever '54 connects pipe 42 through 4-way valve 44 to .pipe 48 and pipe 45 through -4-way valve and 3-way valve ,49 to a pipe 51 discharging into the reservoir 99A: With the lever 54 in the shifted position the piston 39, and. accordingly the carriage 1, will be positioned to the left as shown in Fig. l at maximum speed. Upon the tool reaching the extreme left position, it'will again be brought into engagement with the work piece and the rack 21 brought into mesh with I the differential gear l1, and another cutting stroke started by shifting the lever 54- back to stop 55. f

I CI

In Fig. 3 I show a modified form of pilot mechanism which may be employed in place of the pilot mechanism shown in-Fig. 2. Referring to Fig. 3, I show-the projection 28 pivotally connected to a bell crank- 69. As the projection 28 l is moved inwardly or outwardly by virtue of nected to the bell crank 60 is a movable valve member'62 of a, pilot valve 63. The pilot valve is supplied with a suitable fluid under pressure. such aseompressed air, through an inlet'port 64,

and which is continuously discharged tothe atmosphere at either end of the pilot valve. The movable valve member 62 is provided with a restriction 65 normally pbsitioned adjacent an outlet port 66.. A pressure gradient is established across the restriction 65 and the pressure existing at the outlet port 66 will depend upon the position of the restriction 55 relative to the outlet port. In general, it may. be said that the pilot valve 33- establishes a loading pressure at the outlet port 66 corresponding to the position of the movable valve member 62, and accordingly to the position of the projection 28.

' The loading pressure established at the outlet port 66 is transmitted through a. pipe 61 to a standardizing relay 68 of the type illustrated and described in United States Patent No, Re. 21,804 dated May 20, 1941, to Harvard H. Gorrle.

The standardizing relay 6B acts to establish within a control chamber 69 changes in pressure corresponding to changes in pressure within a loading chamber 19 to which the pipe 61 is con-' tion of the work piece 14. Upon an increase or decrease in speed, of the carriage 1 the loading pressure established -by the pilot 63; will increase or decrease proportionately. The relay 68 will then act to establish an immediate and proportionate change in pressure within the control chamber 59, and thereafter a, slow continuing change until the pressure. within the loading chamber 10 is, restored to the predetermined value. F

device andcomprises two pair of pressure sensi- .tive chambers separated by dlaphragms 1| and 12. Within the chamber 69 is a fulcrum lever 13 adapted when tilted in one direction from the horizontal position to actuate a fluid pressure supply valve 14 (connected to any suitable source of pressure fluid not shown) to admit fluid pressure to the chamber 69, and when tilted in opposite direction to actuate an atmospheric exhaust Tlalve 15- to discharge pressure fluid therefrom.

The diaphragms 1| and .12 are connected together for simultaneous movement by a member 16 secured at its upper end to a manually ad- 'justable loading spring 11' and arranged when moved downwardly from the position shownto cause the supply valve 14 to open, and when moved upwardly to cause the exhaust valve 15 to open.- The chambers separated by the diaphragm 12 are-in communication through an adjustable bleed valve 18. Assuming for example that nor- The relay 98 is essentially a pressure'balancing mal pressure exists within chamber 10, then equal pressures will exist within thechambers separated by the diaphragm 12. Upon an increase in pressure within the chamber the movable member 16 will move downwardly, causing a proportionate increase in pressure within chamber 69. Thereafter, by virtue of the bleed valve 18, the pressure in chamber 69 will continueto increase until the pressure within chamber 10 is restored to the normal value.

, upon departure therefrom will increase or decrease the speed thereof from that desired to compensate for the amount lost while the speed thereof was other than that desired. This speed compensation is accomplished by the differential pressures created in the chambers 69 and 10 and the attendant movement of member 16 that is transmitted to the bellows 38 through pipe 31 which, as before described controls the rate of flow of fluid to the piston 39. In this manner,

notwithstanding momentary departures in speed of. the carriage 1 from that desired, a uniform number of threads per unit length will be cut on Vance at a rate of speed proportional to the rate of rotation of the drive shaft 24. If this rateof advance corresponds to the rate of movement of the carriage 1 then normal distance will be maintained between the bafile 80 and nozzle 84. However, if a change in the rate, of movement of the carriage 1 occurs, then by virtue of the springs 85 the nozzle 84 will approach toward or recede from the battle 80, causing a corresponding change in pressure within pipe 81 which will cause, through 'servomotor l2, a change or restoration in the rate of speed of the carriage 1 to that desired.

While in accordance with the patent statutes I have described certain embodiments of my invention, it is evident that such embodiments may be modified in many ways without departing from the spirit and scope of the invention. Such embodiments of my invention as I have chosen to describe should therefore be taken as merely illustrative and not as limiting.

What I claim as new, anddesire to secure by Letters Patent of the ,UnitedStates, is:

1. In combination with a machine tool having means for rotating a work piece and a carriage movable relative to the work piece, means comprising an externally threaded member rotated in accordance with the speed of rotationof the work piece, means comprising an internally threaded member meshing with said externally threaded member rotated in accordance with the rate of movement of the carriage relative to the work piece, and meansincluding a fluid jet discharging to atmosphere under the joint the work piece 14. In the'embodiment of my invention shown in Fig. 2 where the speed of the carriage 1- will be maintained at that desired; momentary departures in speed from that desired will not be compensated for, so that slight variations in the number of threads per unit of length of the work piece l4 may occur. Under ordinary circumstances such minor variations are immaterial, howeverfin exceptional cases I mayflnd it preferable to employ the pilot mechanism shown in Fig.3 rather than that shown in Fig. 2.

In Figs. 5 and 6 I illustrate a further embodiment of my invention employinga modified form of pilot mechanism. In Fig. 5 I show the lathe I in elevation and 'mounted on the carriage 1 a stationary bailie 80. .Also carried by the carriage 1 in suitable ways 8| is a slide 82' on which is mounted a post 83 carrying a nozzle I. slide is urged toward the baflie' 80 by tension springs 85.

The nozzle 8] is supplied with compressed air from any suitable source through an orifice 88 and a pipe 81. Solong as the nozzle 84 moves at a rate of speed corresponding to that of the carriage 1 the arrangement is such that normal pres sure will exist within pipe 81. If however the nozzle 84 varies in speed from that of the carriage 1 and approaches or recedes'from the ballle II, a

corresponding change in pressure will occur within the pipe 81. The pressure in pipe 81 is'transmitted tothe bellows 38 as shown in Fig. 4, and operates to control the rateof operation of the carriage 1 as heretofore described.

The nozzle 84 moves at a rate ofspeed in desired'proportionality to the rate of speed of the drive shaft 24 rotating the work piece ll. As

. shown, the drive shaft 24 is connected to a sprocket 88 through suitable change and spur gears diagrammatically illustrated at It. Meshing-with the sprocket 88 is a suitable perforated tape ll connected to the slide l2. As the sprocket ll rotates, thetape permit slide 82 to ad- The' control of said last two named means for controlling the rate of movement of said carriage.

2. In combination with a machine tool having means for relatively moving a tool and work piece in two directions, mechanical differential means positioned in accordance with the difference in relative speeds 'in the-two directions, and means including a fluid jet discharging to atmosphere under the control of said differential means for controlling the speed in one direction.

3. In combination with a lathe having a rotatable live center and a movable carriage, a nozzle having a port through which compressed air is continuously discharged to atmosphere, a baflle for said nozzle, the relative approach and 1 recession of said nozzleand bafile governing the pressure of the compressed air in the nozzle,

movement of said carriage per revolution of the live center, and means responsive to the pressure in-said nozzle for governing the rate of movement of said carriage.

4. In combination with a lathe having a rotatable live center and a movable carriage, a

hydraulic motor for moving said carriage, a control couple mova'ble with, said carriage, said control couple comprising a' stationary baflle and a movable fluid nozzle discharging at a con stant rate normally positioned in fixed relation to said baffle, the position of said fluid nozzle with relation to the stationary baille varying in ac-' cordance with changes in the movement of said carriage per revolution of the live center, and

" means responsive to changes in rate of discharge of the fluid nozzle for governing the rate of ment of said hydraulic motor.

5. In combination with a machine tool having means for rotating a work piece and a carriage movable. relative to the work piece, means posimovetioned in accordance with the speed of rotation of the work piece, means positioned in accord H I 8,872,428 ance with the rate or movement of the carriage relative'to the work piece, and means including a fluid jet discharging to atmosphere under the joint control of said last two named means for controlling the rate of movement of said carriage,

6. In combination with a machine tool having means for rotating a work piece and having a carriage movable relative to the work piece, a fluid bleed valve arranged to discharge fluid to the atmosphere, means sensitive to the relation 10' behind the valve.

between speed of rotation of said work piece and speed of carriage movement to vary the rate of fluid discharge from said bleed valve upon departure pf said relation from a desired relation, said fluid ;bleed valve and said sensitive means being so constructed and arranged that the pressure of. the fluid behind the valve varied with the rate of such discharge, and means for moving the carriage responsive to the fluid pressure CLARENCE JOHNSON. 

